[sdiy] Compensating output level for Q

[Richie Burnett]

> I see D30 and D31 in the SH-101 schematics, so I could try that.  Looks 
> easy enough.  I don't know what an equivalent diode is to that: 1s2473. 
> I'll look it up online if you don't have a suggestion.
> The 101 has other parts between the Q wiper and the diodes though, TR26 
> and TR27, etc.  I don't know what those do.... 
> http://manuals.fdiskc.com/flat/Roland%20SH101%20Service%
> 20Manual.pdf page 9

I'm not immediately sure what they're doing either.  Take a look at the 
SH-09 service notes, that are easier to follow.  That shows two back-to-back 
signal diodes connected from the wiper of the resonance pot to ground.  You 
can use any signal diodes you want here like 1N4148, 1N914 etc,  You can 
play about with the resistor values surrounding this diode clipper to set 
the level at which the self-oscillation settles out.  Although as an owner 
of an SH-09 I can say that the filter still sounds quite loud when it self 
oscillates!  But, I think this is quite common behaviour for analogue 
monosynths?

Another thing you can try is to increase the amplitude of the oscillator 
signals driving the filter.  However, this will increase distortion in the 
filter so it might noticeably alter the sound when the filter isn't self 
oscillating.

-Richie,